To determine which of the statements is incorrect, we will analyze each statement one by one.
### Step 1: Analyze the first statement
**Statement:** Albumin is a simple protein.
- **Explanation:** Simple proteins are composed solely of amino acids. Albumin is indeed a simple protein because it consists only of amino acids and does not have any additional groups attached. However, the statement claims that albumin is present around egg yolk, which is misleading. Albumin is primarily found in egg white (not yolk). Therefore, while it is true that albumin is a simple protein, the context of its presence makes this statement misleading.
### Step 2: Analyze the second statement
**Statement:** Amino acid alanine contains an acidic side chain.
- **Explanation:** The general structure of an amino acid includes an amino group, a carboxyl group, a hydrogen atom, and a variable R side chain. In the case of alanine, the R side chain is a methyl group (–CH3). This methyl group is non-polar and neutral, meaning it does not contain an acidic group. Therefore, the statement that alanine contains an acidic side chain is incorrect.
### Step 3: Analyze the third statement
**Statement:** Muscle contains protein keratin.
- **Explanation:** Keratin is a structural protein found in hair, nails, and skin, but it is not found in muscle tissue. The primary protein in muscle tissue is myosin, which is responsible for muscle contraction. Thus, this statement is also incorrect.
### Conclusion
After analyzing all three statements, we find that:
1. The first statement is misleading but can be considered correct in the context of defining albumin as a simple protein.
2. The second statement is incorrect because alanine does not have an acidic side chain.
3. The third statement is incorrect because keratin is not found in muscle tissue.
Thus, the incorrect statements are the second and third statements.
### Final Answer
Both statements 2 and 3 are incorrect. Therefore, the correct answer is option D.
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